Effect of radiotherapy after breast-conserving surgery on 10-year recurrence and 15-year breast cancer death: meta-analysis of individual patient data for 10 801 women in 17 randomised trials

BACKGROUND: After breast-conserving surgery, radiotherapy reduces recurrence and breast cancer death, but it may do so more for some groups of women than for others. We describe the absolute magnitude of these reductions according to various prognostic and other patient characteristics, and relate the absolute reduction in 15-year risk of breast cancer death to the absolute reduction in 10-year recurrence risk. METHODS: We undertook a meta-analysis of individual patient data for 10,801 women in 17 randomised trials of radiotherapy versus no radiotherapy after breast-conserving surgery, 8337 of whom had pathologically confirmed node-negative (pN0) or node-positive (pN+) disease. FINDINGS: Overall, radiotherapy reduced the 10-year risk of any (ie, locoregional or distant) first recurrence from 35.0% to 19.3% (absolute reduction 15.7%, 95% CI 13.7-17.7, 2p/=20%), intermediate (10-19%), or lower (<10%) absolute reductions in the 10-year recurrence risk. Absolute reductions in 15-year risk of breast cancer death in these three prediction categories were 7.8% (95% CI 3.1-12.5), 1.1% (-2.0 to 4.2), and 0.1% (-7.5 to 7.7) respectively (trend in absolute mortality reduction 2p=0.03). In the few women with pN+ disease (n=1050), radiotherapy reduced the 10-year recurrence risk from 63.7% to 42.5% (absolute reduction 21.2%, 95% CI 14.5-27.9, 2p